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Regulatory Assets and Liabilities (ROE of People Gas System Division) (Details) $ in Millions, $ in Millions |  | 1 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 12, 2018 USD ($) | Jan. 31, 2019 USD ($) | Dec. 31, 2018 CAD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2012 USD ($) km | Dec. 31, 2017 CAD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Regulatory Assets |  |  | $ 1,569 |  |  |  | $ 1,411
Regulatory Assets, Current |  |  | 165 |  |  |  | 138
Environmental remediations [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Regulatory Assets |  |  | $ 31 |  |  |  | $ 41
Peoples Gas System Division [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  | 10.75% |  |  |  |
Length Of Pipeline, percentage |  |  |  |  |  | 5.00% |
Length Of Pipeline | km |  |  |  |  |  | 800 |
Amortization of Regulatory Asset | $ 11 |  |  |  |  |  |
Replacement program |  |  |  |  |  | $ 80 |
Regulatory Asset Amortization Period |  |  |  |  |  | 10 years |
Peoples Gas System Division [Member] | Subsequent Event [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Public Utilities Allowed Rate Base |  | $ 12 |  |  |  |  |
Increase (decrease) depreciation rates |  | $ (10) |  |  |  |  |
Peoples Gas System Division [Member] | Environmental remediations [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Reduction in annual depreciation |  |  |  | $ 16 |  |  |
Regulatory Assets |  |  |  |  | $ 32 |  |
Regulatory Assets, Current |  |  |  |  | 21 |  |
Depreciation |  |  |  | $ 5 | $ 16 |  |
Peoples Gas System Division [Member] | Maximum [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  | 11.75% |  |  |  |
Public Utilities, Approved Equity Capital Structure, Percentage |  |  | 54.70% |  |  |  |
Peoples Gas System Division [Member] | Minimum [Member] |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |
Public Utilities, Approved Return on Equity, Percentage |  |  | 9.25% |  |  |  |

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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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